Is it much mor awkward working on 3 phase

[sparkticus]

Not to any standard, in fact if a cable is used it will be a 3 phase type with brown, black grey.
It's not unknown to connect two of the cores to the same phase.
I've never seen notices so the only way to tell is by testing and not assuming

Thanks, I assume there would be two service fuses and a split phase meter?
(perhaps a three phase meter)

 

[Paul_C]

Not the greatest quality I'm afraid, as they were taken with a tiny pocket camera some years ago, but here's a 3-wire 240/480V system (in fact it's that same one on Chapel Rd. that I posted links to above).

Note the single-phase HV spur feeding the transformer (and continuing on to somewhere else), and the two fuses on the secondary, one for each live outer:

 

[sparkticus]

Thanks Paul_C, are those fuses 100A? BS1361s?

 

[Paul_C]

Not sure, as I'm not a distribution network guy. I would have thought they're probably a little larger than that and possibly BS88. Westie will probably be able to fill in the details a little better.

 

[westie101]

those fuses 100A? BS1361

More likely BS88-5 200A or 250A (it looks like a 100kVA transformer so 50kVA per phase)
The fuse carriers are rated up to 400A

 

[ban-all-sheds]

Just remember your safe isolation procedure involves a ten point test.

10?

 

[sparkticus]

those fuses 100A? BS1361

More likely BS88-5 200A or 250A (it looks like a 100kVA transformer so 50kVA per phase)
The fuse carriers are rated up to 400A

Oh right, of course the transformer may well be supplying a number of properties or a farm etc.

This has been a very interesting thread, thank you very much.

 

[ericmark]

Oh dear. Seems I started something? All I was trying to point out is there are many systems and we have to be aware they exist.

In around 40 years I have only worked on an IT system once on a Tunnel boring machine. But we need to be aware just in case.

I saw not just one electrician but a number try to trace faults by comparing the voltage to earth.

Once one leaves the comfort zone of the domestic one does find the odd which can catch one out. I got called to a motor which was repeated tripping the overload on start up. I was forth guy to look at it. Problem was lack of oil in dash pot. Such an easy fault to cure but it had foxed three guys who had no idea what a dash pot was.

 

[flameport]

Just remember your safe isolation procedure involves a ten point test.

10?

Presumably referring to the number of places to check for voltage (or rather lack of) using a 2 probe voltage indicator.
L1-L2
L1-L3
L2-L3
L1-N
L2-N
L3-N
L1-E
L2-E
L3-E
N-E

 

[RF Lighting]

Just remember your safe isolation procedure involves a ten point test.

10?

L1 - L2
L1 - L3
L1 - N
L1 - E
L2 - L3
L2 - N
L2 - E
L3 - N
L3 - E
N - E

 

[westie101]

L1 - L2
L1 - L3
L1 - N
L1 - E
L2 - L3
L2 - N
L2 - E
L3 - N
L3 - E
N - E

Prove the tester works before starting and re prove it at the end! (well we have to!)

 

[sparkticus]

Oh dear. Seems I started something? All I was trying to point out is there are many systems and we have to be aware they exist.

Glad you did as it turned into an interesting distraction.

 

[ban-all-sheds]

That what what I first worked out.

Then I was unable to explain why if L1-L2=0 and L2-L3=0, L1-L3 would not also be 0.

If they were done first, and you knew that L1=L2=L3, you'd only need to do one Ln-E and one Ln-N.

And if they were both 0, N-E would be redundant.

5 tests.

 

[riveralt]

That what what I first worked out.

Then I was unable to explain why if L1-L2=0 and L2-L3=0, L1-L3 would not also be 0.

If they were done first, and you knew that L1=L2=L3, you'd only need to do one Ln-E and one Ln-N.

And if they were both 0, N-E would be redundant.

5 tests.

The ten point test system was drummed into us at college for the 2391 course - we were warned if we did not follow the ten point test system then we would fail the course - so I never do short cuts, even if you can do it in five, bas.

The reason being is that it is easier to learn one system for three phase than two - you would use the ten point system for IR tests and Polarity live as well.

 

[ban-all-sheds]

The ten point test system was drummed into us at college for the 2391 course.

Kinda implies that they drummed out any real understanding of what you were doing?